Bicycle Gear Mechanism

ABSTRACT

A derailleur ( 10 ) is predisposed to translate a drive change ( 11 ) between at least two gears ( 12 ) rotating about a rotation axis (y). The derailleur ( 10 ) is mobile in one direction in rotation with respect to the bicycle frame by action of a cable ( 14 ) which by command is made to exert a traction force. In an opposite direction the derailleur ( 10 ) rotates, also by action of the cable ( 14 ), which is loosened by command, and by action of elastic means. The gear change comprises a retaining device ( 2 ) predisposed to maintain the derailleur ( 10 ), in absence of a command, in a predetermined angular position. The retaining device ( 2 ) comprises a fixed portion and a mobile portion. The fixed portion is associable to the bicycle frame, the mobile portion is solidly associable to the derailleur ( 10 ). The fixed portion, in determined angular positions of the derailleur ( 10 ), removably connects to the mobile portion.

TECHNICAL FIELD

The invention relates to the field of gears for bicycles.

BACKGROUND ART

Known-type bicycle gears comprise a derailleur provided with an elementfor guiding a bicycle transmission chain. The derailleur is connected tothe frame of the bicycle and is predisposed to rotate, on command, withrespect to the bicycle frame in order to translate the chain between aplurality of coaxial gears on a wheel of the bicycle rotating about anaxis thereof. The axis, in the case of a front gear change, is therotation axis of the central movement, i.e. the pedals, while in aposterior change the rotation axis is that of the rear wheel.

The derailleur comprises an arm to which the chain guide element isassociated. The arm is typically constituted by a four-bar hinge inwhich two parallel sides are defined respectively by a connectionelement to the bicycle frame and an element to which the chain guideelement is connected. The two arms of the four-bar hinge, which connectthe frame connection element and the chain guide element, are arrangedin such a way as to allow displacements of the chain guide element in atransversal direction with respect to the drive chain.

The chain guide element is defined by a cage which, in the case of arear change, supports two cogwheels lying on a plane that isperpendicular to the rotation axis of the gears.

The function of the four-bar hinge, or more generally the arm supportingthe chain guide element, is to guarantee that the guide element of thedrive chain can displace parallel to itself with respect to the bicycleframe. In particular, the chain guide element displaces, maintaining aconstant orientation of the connection element with the bicycle frame.

The displacements of the chain guide element are determined by means ofa cable connected by an end thereof to at least one of the arms of thefour-bar hinge, and connected at another end thereof to a command,usually associated to the bicycle frame, which enables the cable to bepulled or released by winding it or unwinding it onto or off a drum. Bycreating traction on the cable a rotation of the arms of the four-barhinge is determined with respect to the relative hinging points with theconnection element, while on releasing the tension on the cable, aspring induces an opposite rotation of the arms. The derailleur ismobile in a plurality of angular positions in each of which the drivechain enmeshes with a gear. Each angular position is defined by atraction or release of a predetermined length of the gear changeactivating cable. For this purpose the command by which the pulling orreleasing action is performed is provided with a selector mechanismwhich impresses on the drum the cable winds on a rotation by apredetermined angle for each action performed on the command. Themechanism generally comprises a rotary transmission includingsingly-directed retaining elements which enable a rotation of the drumto be made, maintaining the drum in the position reached in the absenceof further commands.

Known-type commands exhibit several drawbacks. The selector mechanism isarranged internally of the command, which is therefore rather complex inconstruction. Indeed a large number of components are needed to realisedthe selector mechanism. The synchronisation of the drum rotation withthe rotation of the derailleur is done by the cable and the sheaththereof, which are provided with a degree of elasticity. There is infact a certain amount of play between the two elements. In order toperform the synchronisation, once the cable is joined up to the commandand the derailleur, it is necessary to position the drum and thederailleur in a “zero” initial position. This operation is performed byvarying the position of one of the ends of the sheath by means of ascrew adjustment. By effectively “lengthening” the sheath the cable istensed, and by effectively “shortening” the sheath the cable isloosened. This is a somewhat laborious operation which can be performedonly with the bicycle mounted on a special support, raised from theground and with the back wheel free to rotate. Once calibrated, furtheradjustments will be necessary as loads and therefore deformations whichthe various elements are subject to are greater when the bicycle is atwork, and a pre-calibration with the cycle at rest is very difficult toachieve. Should there be a tiny variation in the axial distance betweenthe various gears, a new gear change mechanism adjustment operation isrequired.

The main aim of the present invention is to provide a gear changemechanism for a bicycle which will obviate the drawbacks of the priorart.

An advantage of the invention is that the gear change is extremelyprecise and reliable during operation.

A further advantage thereof is that it enables use of extremely simpleand economical gear controls.

A further advantage is that the gear change is very simply and rapidlyadjusted.

DISCLOSURE OF INVENTION

Further characteristics and advantages will better emerge from thefollowing detailed description of a gear change for a bicycle, madeherein below with reference to the accompanying figures of the drawings,given purely by way of a non-limiting example, in which:

FIG. 1 is a perspective view in partial section of a gear change of thepresent invention;

FIG. 2 is the same perspective view as in FIG. 1, with some partssectioned;

FIG. 3 is a detail of the gear change mechanism of the invention withsome parts removed in order better to evidence others.

With reference to the figures of the drawings, the gear change of thepresent invention comprises a derailleur 10, associable to a frame of abicycle, predisposed to translate a transmission chain 11 between atlest two gears 12 rotating about a first rotation axis y. The chain 11is represented schematically, in a broken line, in the figures forreasons of simplicity. The rotation axis can be the axis of the rearwheel, if the gear change is posterior, or can be central i.e. therotation axis of the pedals, should the gear change be fitted to theclanger. The solution illustrated in the present description relates, byway of an example, to a rear wheel-mounted gear change.

In greater detail, the derailleur 10 comprises a hook portion 18,solidly associable to the bicycle frame, and a connecting portion 17,which rotates with respect to the hook portion 18 about a secondrotation axis z. In the illustrated solution, i.e. a rear wheel mountedgear change, the second rotation axis z is parallel to the firstrotation axis y. In the case of a front mounted gear change, the secondrotation axis z is transversal with respect to the first rotation axisy.

On command the derailleur 10 is mobile in rotation, with respect to thebicycle frame, about a main axis x between at least two angularpositions, in each of which the drive chain 11 enmeshes with a gear 12.In one direction the derailleur 10 is mobile in rotation by means of acable 14 which at an end 14 a thereof is solidly constrained to thederailleur 10 and is subjected to a traction force by means of a commandof known type and not illustrated in the figures. In an oppositedirection, the derailleur is mobile in rotation by means of a cable 14which is loosened by means of the above-mentioned command, and also byelastic elements of known type and not represented in the figures of thedrawings. The gear change comprises a retaining device 2, predisposed tokeep the derailleur 10, in the absence of commands, in one of the atleast two positions. The retaining device 2 comprises a fixed portionand a mobile portion. The fixed portion is associable to the bicycleframe, solid in rotation about the main axis x of the derailleur 10,while the mobile portion is solidly associable to the derailleur 10. Thefixed portion, in the at least two angular positions of the derailleur10, is removably connected to the mobile portion.

The mobile portion, associable to the derailleur 10, comprises acylindrical sector 3, which has at a lateral surface thereof at leasttwo chambers 4. The cylindrical sector 3 is coaxial to the main axis xof the derailleur 10. the cylindrical sector 3 exhibits, on a lateralsurface thereof, a channel which develops coaxially to the cylindricalsector 3 itself. The channel is predisposed to receive at least onetract of the cable 14 which is adjacent to the end 14 a that is solidlyconstrained to the derailleur 10. The cable 14, over a tract of itslength close to the end 14 a, is arranged tangentially in contact withthe cylindrical sector 3.

The fixed portion, associable to the bicycle frame solidly in rotationabout the main axis x of the derailleur 10, comprises a shaped element 5which is mobile within a housing 6 that is afforded in an appendage 16of the connecting portion 17. The housing 6 exhibits an elongate shapeand is open at an end that is close to a lateral surface of thecylindrical sector 3. Internally of the housing 6 elastic means arearranged to push the shaped element 5 into contact with the lateralsurface of the cylindrical sector 3.

In a preferred embodiment, the shaped element 5 is a sphere. The elasticmeans are a flat spring 8 which at an end is in contact with the sphere.The flat spring 8 is arranged parallel to the housing 6 and at an endthereof is constrained to the appendage 16 of the connecting portion 17,while at another end it is located in contact with the shaped element 5in order to exert, on the shaped element 5, a force directed radiallywith respect to the cylindrical sector 3. In some determined angularpositions of the derailleur 10, the shaped element 5, or sphere, engagesat least partially in the chambers 4 arranged on the lateral surface ofthe cylindrical sector 3 by effect of the push exerted by the flatspring 8. The force with which the sphere 5 is pressed towards a chamber4 is sufficient, in the absence of commands of the cable 14, to maintainthe derailleur 10 in a corresponding angular position with respect tothe main rotation axis x. In order to impose a rotation in a givendirection to the derailleur 10 the cable must be activated 14 intraction up until it exerts a force which is superior to the forcedetermined by the engagement of the sphere 5 in a chamber 4. To imposean opposite rotation on the derailleur 10, the cable 14 is loosened; theelastic means of known type, by means of which the derailleur 10 ismobile in rotation, are of such a size as to exert a couple, withrespect to the main axis x, which is sufficient to overcome the coupledetermined by the engagement of the sphere 5 in a chamber 4. Toestablish an initial, or zero position of the derailleur 10, theappendage 16 is slidable with respect to the connecting portion 17,either towards or away from the cylindrical sector 3 along a windingdirection of the cable 14 on the cylindrical sector 3. A sliding of theappendage 16 is equivalent, in practice, to a modification of the cablelength 14; by nearing the appendage 16 to the cylindrical sector 3 thederailleur 10 rotates in a direction, while by distancing the appendage16 from the cylindrical sector 3, the derailleur 10 rotates in anopposite direction. Thus, by sliding the appendage 16, a calibration ofthe initial derailleur position is possible. The appendage 16 isslidable with respect to the connecting portion 17 by means of a deviceof known type constituted by a screw which is axially constrained to theappendage 16, and by a nut, solidly connected to the connecting portion17.

The bicycle gear change mechanism of the invention offers importantadvantages.

Firstly, it is precise and reliable. As the retaining device isassociated to the derailleur, the gear change enables the use ofextremely simple and economical commands which are limited to winding-onand off the cable for tracts of the length thereof which do not go abovea determined amount. The calibration of the gear change is very simpleand rapid as the retaining device and the derailleur are not separatedby the presence of the cable and the sheath. Thus the position of thederailleur is determined directly by the retaining device, with noinfluence due to the elasticity of the cable and sheath.

1. A bicycle gear mechanism, comprising a derailleur (10), associable toa bicycle frame, predisposed to translate a drive chain (11) between atleast two gears (12) rotating about a rotation axis (y), the derailleur(10) being on command mobile in rotation about a main axis (x) withrespect to the bicycle frame between at least two angular positions, ineach of which positions the drive chain (11) enmeshes with a gear (12),the derailleur (10) being mobile in rotation in one direction by actionof a cable (14) which is caused to exert a traction force on thederailleur (10), and being mobile in another direction by action of thecable (14) which is on command caused to release a traction on thederailleur (10), wherein the gear mechanism comprises a retaining device(2) which in absence of a command is predisposed to keep the derailleur(10) in one of at least two positions, the retaining device (2)comprising a fixed portion and a mobile portion, the fixed portion beingassociable to the bicycle frame solidly in rotation about the main axis(x) of the derailleur (10), the mobile portion being solidly associableto the derailleur (10); the fixed portion, at the at least two angularpositions of the derailleur (10), removably connecting to the mobileportion.
 2. The gear change mechanism of claim 1, wherein the mobileportion, associable to the derailleur (10), comprises a cylindricalsector (3) which is coaxial to the main axis (x) of the derailleur (10),which cylindrical sector bears at least two chambers (4) on a lateralsurface thereof.
 3. The gear change mechanism of claim 2, wherein thefixed portion, solidly associable to the bicycle frame, comprises ashaped element (5) which is mobile internally of an elongate housing (6)which is open at an end thereof which is proximal to the lateral surfaceof the cylindrical sector (3), elastic means being arranged internallyof the housing (6) in order to push the shaped element (5) into contactwith the lateral surface of the cylindrical sector (3).
 4. The gearchange mechanism of claim 3, wherein the shaped element (5) is definedby a sphere, the elastic means being defined by a flat spring (8) whichat an end thereof is placed in contact with the sphere.
 5. The gearchange mechanism of claim 1, wherein the derailleur (10) comprises ahook portion (18), solidly associable to the bicycle frame, and aconnecting portion (17) which rotates with respect to the hook portion(18) about a second rotation axis (z), wherein the housing (6) is madein an appendage (16) of the connecting portion (17), the flat spring (8)being arranged parallel to the housing (6), the flat spring (8) beingconstrained at an end thereof to the appendage (16) of the connectingportion (17), being constrained at another end thereof being placed incontact with the shaped element (5) in order to exert a force on theshaped element (5) which force is directed radially with respect to thecylindrical sector (3).
 6. The gear change mechanism of claim 5, whereinthe appendage (16) is slidable with respect to the connecting portion(17) both in a nearing and in a distancing direction with respect to awinding direction of the cable (14) onto the cylindrical sector (3). 7.The gear change mechanism of claim 1, wherein the cylindrical sector (3)exhibits, on a lateral surface thereof, a channel which developscoaxially to the cylindrical sector (3), the channel being predisposedto receive at least a tract of the cable (14).